Enhanced anaerobic biotransformation of carbon tetrachloride with precursors of vitamin B₁₂ biosynthesis

Relatively low concentrations of Vitamin B₁₂ are known to accelerate the anaerobic biotransformation of carbon tetrachloride (CT) and chloroform (CF). However, the addition of vitamin B₁₂ for field-scale bioremediation is expected to be costly. The present study considered a strategy to generate vitamin B₁₂ by addition of biosynthetic precursors. One of the precursors, porphobilinogen (PB) involved in the formation of the corrin ring, significantly increased the CT biotransformation rates by 2.7-, 8.8- and 10.9-fold when supplemented at 160, 500 and 900 μM, respectively. A positive control with 10 μM of vitamin B₁₂ resulted in a 5.9-fold increase in the CT-bioconversion rate. PB additions provided high molar yields of inorganic chloride (57% of CT organochlorine), comparable to that obtained with vitamin B₁₂ supplemented cultures. The primary substrate, methanol, known to induce vitamin B₁₂ production in methanogens and acetogens, was required for PB to have a significant impact on CT conversion. The observation suggests that PB's role was due to stimulating vitamin B₁₂ biosynthesis. The present study therefore provides insights on how to achieve vitamin B₁₂ enhanced rates of CT bioremediation through the use of less complex compounds that are precursors of vitamin B₁₂. Although PB is a costly chemical, its large impact points to corrin ring formation as the rate-limiting step.